Impact of iron-modified fillers on enhancing water purification performance and mitigating greenhouse effect in constructed wetlands.

Abstract

Iron is gradually being introduced into constructed wetlands (CWs) to enhance the removal of pollutants due to its active chemical properties and ability to participate in various reactions, but its effectiveness in greenhouse effect control needs to be studied. In this study, three CWs were established to evaluate the effect of iron scraps and iron-carbon as substrates on pollutants removal and greenhouse gas (GHG) emissions, and the corresponding mechanisms were explored through analysis of microbial characteristics. The results showed that iron scraps and iron - carbon are effective in enhancing the effluent quality of CWs. Iron-carbon exhibited notable efficacy in removing nitrate nitrogen (NO₃^--N) and chemical oxygen demand (COD), achieving stable removal rates of 98.46% and 84.89%, respectively. Iron scraps had advantages in promoting the removal of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN), with removal rates of 43.73% and 71.56%, respectively. The emission fluxes of nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) had temporal variability, always peaking in the early phases of operation. While iron scraps and iron-carbon effectively reduced the average emission flux of N₂O and CO₂, they simultaneously increased the average emission flux of CH₄ (from 0.2349-2.2698 and 1.1956mg/m²/h, respectively). From the perspective of reducing global warming potential (GWP), iron - carbon had superior performance (from 146.2548-86.7447 mg/m²/h). In addition, the greenhouse gas emission flux was closely related to the microbial community structure in CWs, particularly with a more pronounced response observed in N₂O emissions.